People change OP and sometimes not for the better. It's saddening and shocking when that happens because we love and rely on them. You have to accept though that he's changed and won't change back for you or your baby.
Just from what you've said here, look at this (and I suspect this isn't everything he's done):
He left you and his child
He tried to emotionally manipulate and pressure you into an abortion
He was completely disrespectful and vile by spitting in your face when you said no
You are happier and more relaxed without him around.
You kept him in the loop about the baby, he doesn't care, doesn't want to know and not only showed no interest but told you so to your face!
He knows his behaviour is shitty, he knows people will judge him for it so he's tries to pressurise you into staying away from his family. He tries to lose you support you need and your baby that loving connection with his grandparents.
He verbally abused you.
He verbally abused you in public. What does he do and what could he do in private?
He is contradictory, either playing mind games or far too messed up to be any kind of reliable or responsible or good influence for a child.
He acts like a petulant child.
He's trying to manipulate you into getting what he wants, which isn't healthy for you at all.
He tries to control you and has you thinking you can't even post what you want on your own facebook.
You may say you adore the man to bits but he is not the same man you once knew. Seeing everything he has down written down here, do you really think he's good for you or your son? Do you want such bad behaviour with him picking up and dropping your son? Maybe even saying he doesn't want him to him?
I think you would be doing yourself such a disservice to continue any kind of relationship with him- i think that ship should stay sailed far far away. In fact I would continue contact with his family and cut contact with him. I would make it clear you will tell his mum about the baby and if he wants to know then he can speak to her. His actions speak loudly: he isn't ready and doesn't want to be a dad. You can give him every chance in the world but ultimately you and your son will reap the badness from that because he will not change.
If he changes in the future and steps up then I would think about he and your son having a relationship but I would never, ever consider getting back with someone who has acted so unpleasantly and with such little regard for someone he claimed to love and his own unborn child.
And take him off your facebook, cut contact and post what you want. Do let him control you and stress you out, he really isn't worth it.